THE author reveals some curious facts in this memoir, which from its
unpretending and somewhat indefinite title we fear may be overlooked in
the ever-flowing rush of scientific literature. The main subject
discussed is the extraordinary mimetic resemblance which certain
butterflies present to other butterflies belonging to distinct groups.
To appreciate the degree of dissimulation practised by these insects,
it is necessary to study the beautiful plates with which the memoir is
adorned. In a district where, for instance, an Ithomia abounds
in gaudy swarms, another butterfly, namely a Leptalis, will
often be found mingled in the same flock, so like the Ithomia in
every

shade and stripe of colour and even in the shape of its wings, that
Mr. Bates, with his eyes sharpened by collecting during eleven years,
was, "though always on my guard," continually deceived. When the
mockers and the mocked are caught and compared they are found to be
totally different in essential structure, and to belong not only to
distinct genera, but often to distinct families. If this mimicry had
occurred in only one or two instances, it might have been passed over
as a strange coincidence. But travel a hundred miles, more or less,
from a district where oneLeptalis imitates one Ithomia,
and a distinct mocker and mocked, equally close in their resemblance,
will be found. Coloured drawings of seven mocking forms of Leptalis,
and six mocked forms of Ithomia, and one of another genus are
given. Altogether no less than ten genera are enumerated, which include
species that imitate other butterflies. The mockers and mocked always
inhabit the same region; we never find an imitator living remote from
the form which it counterfeits. The mockers are almost invariably rare
insects; the mocked in almost every case abound in swarms. In the same
district in which a species of Leptalis closely imitates an Ithomia,
there are sometimes other Lepidoptera mimicking the same Ithomia;
so that in the same place, species of three genera may be found all
closely resembling a species of a fourth genus. It is highly remarkable
that even moths, notwithstanding their dissimilarity in structure and
general habits of life, sometimes so closely imitate butterflies (these
butterflies being simultaneously mocked by others) that, as Mr. Bates
says, when "seen on the wing in their native woods, they deceive the
most experienced eye." These several facts and relations carry the
strongest conviction to the mind that there must be some intimate bond
between the mocking and mocked butterflies. It may, however, be
naturally asked, why is the one considered as the mocked form; and why
are the others, or two or three other butterflies which inhabit the
same district in scanty numbers, considered as the mockers? Mr. Bates
satisfactorily answers this question, by showing that the form which is
imitated keeps the usual dress of the group to which it belongs, whilst
the counterfeiters have changed their dress and do not resemble their
nearest allies.

In these facts, of which only a brief abstract has been given, we
have the most striking case ever recorded of what naturalists call
analogical resemblance. By this term naturalists mean the resemblance
in shape, for instance, of a whale to a fish—of certain snake-like
Batrachians to true snakes—of the little burrowing and social
pachydermatous Hyrax to the rabbit, and other such cases. We
can understand resemblances, such as these, by the adaptation of
different animals to similar habits of life. But it is scarcely
possible to extend this view to the variously coloured stripes and
spots on butterflies; more especially as these are known often to
differ greatly in the two sexes. Why then, we are naturally eager to
know, has one butterfly or moth so often assumed the dress of another
quite distinct form; why to the perplexity of naturalists has Nature
condescended

to the tricks of the stage? We remember only one statement, made by
Mr. Andrew Murray in his excellent paper on the Disguises of Nature,1 namely that insects thus imitating each other usually inhabit the same
country, which combined with the fact of the imitators being rare and
the imitated common, might have given a clue to the problem. Mr. Bates
has given to these facts the requisite touch of genius, and has, we
cannot doubt, hit on the final cause of all this mimicry. The mocked
and common forms must habitually escape, to a large extent,
destruction, otherwise they could not exist in such swarms; and Mr.
Bates never saw them preyed on by birds and certain large insects which
attack other butterflies; he suspects that this immunity is owing to a
peculiar and offensive odour that they emit. The mocking forms, on the
other hand, which inhabit the same district, are comparatively rare,
and belong to rare groups; hence they must suffer habitually from some
danger, for from the number of eggs laid by all butterflies, without
doubt they would, if not persecuted, in three or four generations swarm
over the whole country. Now if a member of one of these persecuted and
rare groups were to assume a dress so like that of a well-protected
species that it continually deceived the practised eyes of an ardent
entomologist, it would often deceive predacious birds and insects, and
thus escape entire annihilation. This we fully believe is the true
explanation of all this mockery.

Mr. Bates truly observes, that the cases of one butterfly mocking
another living butterfly do not essentially differ from the innumerable
instances of insects imitating the bark of trees, lichens, sticks, and
green leaves. Even with mammals, the hare on her form can hardly be
distinguished from the surrounding withered herbage. But no case is
known of a deer or antelope so like a tiger as to deceive a hunter; yet
we hear from Mr. Bates of insects more dissimilar than a ruminant and
carnivore, namely, of a cricket most closely resembling a cicindela—averitable tiger amongst insects. Amongst birds, all that
habitually squat on the ground in open and unprotected districts,
resemble the ground, and never have gaudy plumage. It appears, however,
that two cases of birds mocking other birds have been observed by that
philosophical naturalist, Mr. Wallace. Amongst insects, on the other
hand, in all parts of the world, there are innumerable cases of
imitation; Mr. Waterhouse has noted an excellent instance (and we have
seen the specimens) of a rare beetle inhabiting the Philippine
Archipelago, which most closely imitates a very common kind belonging
to a quite distinct group. The much greater frequency of mockery with
insects than with other animals, is probably the consequence of their
small size; insects cannot defend themselves, excepting indeed the
kinds that sting, and we have never heard of an instance of these
mocking other insects, though they are mocked: insects cannot escape by
flight from the larger animals; hence they are reduced, like most weak
creatures, to trickery and dissimulation.

By what means, it may be asked, have so many butterflies of the
Amazonian region acquired their deceptive dress? Most naturalists will
answer that they were thus clothed from the hour of their creation—an
answer which will generally be so far triumphant that it can be met
only by long-drawn arguments; but it is made at the expence of putting
an effectual bar to all further inquiry. In this particular case,
moreover, the creationist will meet with special difficulties; for many
of the mimicking forms of Leptalis can be shown by a
graduated series to be merely varieties of one species; other mimickers
are undoubtedly distinct species or even distinct genera. So again,
some of the mimicked forms can be shown to be merely varieties; but the
greater number must be ranked as distinct species. Hence the
creationist will have to admit that some of these forms have become
imitators, by means of the laws of variation, whilst others he must
look at as separately created under their present guise; he will
further have to admit that some have been created in imitation of forms
not themselves created as we now see them, but due to the laws of
variation! Prof. Agassiz, indeed, would think nothing of this
difficulty; for he believes that not only each species and each
variety, but that groups of individuals, though identically the same,
when inhabiting distinct countries, have been all separately created in
due proportional numbers to the wants of each land. Not many
naturalists will be content thus to believe that varieties and
individuals have been turned out all ready made, almost as a
manufacturer turns out toys according to the temporary demand of the
market.

There are some naturalists, who, giving up to a greater or less
extent the belief of the immutability of species, will say that as the
mocked and mocking forms inhabit the same district, they must have been
exposed to the same physical conditions, and owe to this circumstance
their common dress. What direct effect the physical conditions of life,
that is, climate with all its contingencies and the nature of the food,
produce on organic beings is one of the most abstruse problems in
natural history, and cannot be here discussed. But we may remark that
when a moth closely resembles a butterfly, or better still, when a
cricket resembles a Cicindela, it becomes very difficult to
believe that insects so widely dissimilar in their internal structure
and habits of life, should have had their external organization alone
so largely influenced by their conditions of life as to become almost
identical in appearance. Can we believe that one insect comes to
resemble the bark of a tree; another a green leaf; another in its
larval condition the dead twig of a branch; or that a quail or snipe
comes to resemble the bare ground on which it lies concealed, through
the direct action of the physical conditions of life? If in these
cases, we reject this conclusion, we ought to reject it in the case of
the insects which mock other insects.

Assuredly something further is required to satisfy our minds: what
this something is, Mr. Bates explains with singular clearness

and force. He shows that some of the forms of Leptalis,
whether these be ranked as species or varieties, which mimick so many
other butterflies, vary much. In one district several varieties (which
are figured) occur; one alone of these pretty closely resembles the
common Ithomia of the same district. In a few other cases,
this Leptalis presents two or three varieties, one of which
is much commoner than the others, and this alone mocks an Ithomia.
In several cases a single Leptalis, which sometimes must
be ranked, according to the usual rules followed by naturalists, as a
variety and sometimes as a distinct species, mocks the common Ithomia
of the district. From such facts as these, Mr. Bates concludes
that in every case the Leptalis originally varied; and that
when a variety arose which happened to resemble any common butterfly
inhabiting the same district (whether or no that butterfly be a variety
or a so-called distinct species) then that this one variety of the Leptalis
had from its resemblance to a flourishing and little persecuted
kind a better chance of escaping destruction from predacious birds and
insects, and was consequently oftener preserved;—"the less perfect
degrees of resemblance being generation after generation eliminated,
and only the others left to propagate their kind." This is Natural
Selection. Mr. Bates extends this view, supporting it by many facts and
forcible arguments, to all the many wonderful cases of mimickry
described by him. He adds, "thus, although we are unable to watch the
process of formation of a new race as it occurs in time, we can see it,
as it were, at one glance, by tracing the changes a species is
simultaneously undergoing in different parts of the area of its
distribution."

To the naturalist who is interested with respect to the origin of
species, the most important parts of this Memoir, together with the
descriptive portion at the end, are probably those which treat on the
limits of species, on sexual variation, on the variation of important
characters, such as the neuration of the wings, &c. We cannot here
discuss these points. Mr. Bates shows that there is a perfect gradation
in variability, from butterflies, of which hardly two can be found
alike, to slight varieties, to well-marked races, to races which can
hardly be distinguished from species, to true and good species. Under
this point of view, the history of Mechanitis polymnia well
deserves study: after describing its several varieties, Mr. Bates adds,
"these facts seem to teach us that, in this and similar cases, a new
species originates in a local variety, formed in a certain area, where
the conditions are more favourable to it than to the typical form, and
that a large number of such are simultaneously in process of formation
from one variable and widely distributed species." It is hardly an
exaggeration to say, that whilst reading and reflecting on the various
facts given in this Memoir, we feel to be as near witnesses, as we can
ever hope to be, of the creation of a new species on this earth.

We will only notice briefly one other point which has an important
bearing on the production of new races and species; namely the

statement repeatedly made that in certain cases the individuals of
the same variety evince a strong predilection to pair together. We do
not wish to dispute this statement; it has been affirmed by credible
authors, that two herds of differently coloured deer long preserved
themselves distinct in the New Forest; and analogous statements have
been made with respect to races of sheep in certain Scotch islands; and
we know no reason why the same may not hold good with varieties in a
state of nature. But we are by our profession as critics bound to be
sceptical, and we think that Mr. Bates ought to have given far more
copious evidence. He ought also to have given in every case his reasons
in full for believing that the closely allied and co-existing forms,
with which his varieties do not pair, are not distinct
species. Naturalists should always bear in mind such cases as those of
our own willow wrens, two of which are so closely alike that
experienced ornithologists can with difficulty distinguish them,
excepting by the materials of which their nests are built; yet these
are certainly as distinct species as any in the world.

We think so highly of the powers of observation and reasoning shown
in this Memoir, that we rejoice to see by the advertisements that Mr.
Bates will soon publish an account of his adventures and his
observations in natural history, during his long sojourn in the
magnificent valley of the Amazon. We believe that this work will be
full of interest to every admirer of Nature.1